Heater



FIG. 1 is a right side perspective view of a heater showing the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof; and,

FIG. 4 is a right side view thereof.

Portions of the design shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a heater, substantially as shown and described. 